Gardaí are now investigating whether one of Ireland's most high-profile missing people may have been the victim of foul play.

A renewed appeal is being launched later this week in the mysterious case of Trevor Deely (22), who was last seen walking home from a Christmas party in Dublin city centre in the early hours of December 8, 2000.

A mystery man is now being traced who gardaí believe may have key information about the 16-year-old mystery of the missing Co Kildare man.

It is understood that officers are probing the possibility that tragic Mr Deely may have been pushed into the River Dodder, but this is not conclusive.

"This missing person's case could be upgraded to a suspicious death investigation," a senior source said last night.

Gardaí are now trying to trace a man who waited outside Mr Deely's workplace in the early hours of that morning after he briefly returned to his office on the night of his disappearance.

The new development, which senior sources regard as significant, came about as a result of technological advances in the examination of CCTV footage.

Last December, gardaí began a cold case review, which included reviewing the evidence gathered, reinterviewing witnesses and looking again at CCTV footage gathered as part of the original investigation.

Some of that material, VHS footage taken from outside Bank of Ireland Asset Management on the night he disappeared, was recently sent to the UK to be forensically enhanced.

The new footage shows a man standing outside the bank's office in the early hours of the morning in question.

Mr Deely arrived at the office after finishing his night at Buck Whaley's nightclub on Lower Leeson Street just before 3.30am.

He is seen speaking briefly to the man before he goes into the building.

Mr Deely was a member of the IT department of the bank and when he arrived he was "drowned wet", said his colleague Karl Pender who was working overnight in IT.

He chatted with Mr Pender, briefly logged onto his computer, then went for a coffee with Mr Pender to the office canteen and chatted about the night's Christmas party.

Gardaí are now aware that a man was standing in the doorway of the office, possibly sheltering from heavy rain, as Mr Deely walked in shortly before 3.30am. The man is seen waiting outside for a short time before crossing the road.

When Mr Deely leaves the building after 4am he is carrying an umbrella. The footage then shows a man - who gardaí believe is the same man from earlier - following him.

Gardaí are very keen to speak to this man and hope to identify him as an image of him is set to be released to the public tomorrow.

The last image of Mr Deely shows him walking down Haddington Road under an umbrella he got from the office on what was a very stormy night.

The young bank worker had been in great form that night, according to his colleagues.

It is understood that he was not suffering from depression and was considered a "stable, sensible young man" according to sources.

Details of a new award about the case are expected to be announced at a Crime Stoppers press conference tomorrow.